1. Field of the Invention
The present invention relates to an image reading apparatus for reading image information of a document, and an image forming apparatus including the image reading apparatus.
2. Description of the Related Art
Conventional image reading apparatuses is provided with an automatic document conveyance apparatus (auto document feeder). Specifically, in such an image reading apparatus, an auto document feeder conveys a document onto a slit glass plate, and reads an image on the document while the document is passing through a reading position on the slit glass plate.
In the sheet-through system, an image reading unit fixed on one surface side of an elongated slit glass (transparent member) reads an image on a document by focusing light of an optical reading system on the image bearing surface of the document pass through the other side of the slit glass. Therefore, if a foreign matter, such as dust, adheres on the slit glass, a portion in which light is shielded by the foreign matter shows a streak of image noise in the read image.
Foreign matters adhering to the slit glass include paper powder flying from a document made mainly of paper, floating foreign matters such as dust in the atmospheric air, and adhesive foreign matters, such as a tape's adhesive agent, a peeling of paste, whiteout, and a clot of ball-point pen ink adhering to a document.
Various methods for removing foreign matters on the surface of the slit glass have conventionally been proposed. Among these methods, for example, a certain method utilizes a roller having an elastic member, such as a felt material and foaming material, as a cleaning member on a slit glass plate. The roller is rotatably provided to clean the surface of the slit glass by using the cleaning member to remove foreign matters from the surface of the slit glass (refer to Japanese Patent Application Laid-Open No. 2000-270152).
However, although floating foreign matters can be comparatively efficiently collected, the cleaning member made of an elastic member or a cleaning member composed of a conductive brush connected to the ground can sweep only a glass portion which the elastic member or the hair tip of the brush contacts. Therefore, it is difficult to efficiently remove adhesive foreign matters.
In particular, the effect of sweep decreases as viscosity of adhesive foreign matters decreases. Moreover, once an adhesive foreign matter adheres to the hair tip of the above-described brush-type cleaning member, the adhering foreign matter may return to the glass portion during cleaning by the rotation of the cleaning member, possibly expanding a foreign matter adhering area.
Further, once an adhesive foreign matter adheres to the hair tip of the brush of the brush-type cleaning member, the efficiency of collecting floating foreign matters by an electrostatic method decreases at the portion where the adhesive foreign matter adheres.